The main causes of flooding are:
A storm surge is a change in the sea level caused by a storm such as a hurricane. The main cause of storm surges is high winds pushing the sea water towards the coast causing it to accumulate there. The low pressure at the centre of the storm also contributes towards storm surges ‘pulling’ the water up. The strong storm winds create large waves on top of the surge which can cause damage to coastal sea defences or breach them adding to flood risk. In some cases, there may also be heavy rain increasing the risk of flooding.
rising sea levels
According to recent studies, sea levels are rising by around 4mm per year due to climate change, as ice caps melt and the oceans warm and expand. This steady rise in sea level will not necessarily cause coastal flooding directly in the UK as coastline developments and defences are designed to withstand the larger flow of tides. But the rising level gives a higher starting point for the storm surges and larger waves that can overtop the coastal defences putting more people at risk of coastal flooding.
Many coastal settlements have developed onto what is known as reclaimed land. This is land that has been gained from the sea due to coastal management or ironically, lowered sea levels. This land, although highly valuable, is low lying and flat, so a small rise in the sea level from a mild storm surge is potentially enough to flood it and cause extensive damage.